A PLB certainly is different than an EPIRB.

My PLB has an EPIRB built into it.
Read about them and then you'll know.

here's how they work

PS (this is an edit to the original post above)

So I guess there is a 406Mhz beacon calling itself an EPIRB? I was lead to believe that the old 121's were called EPIRB's and that the 406's were called PLB's.

Therefore, I thought that people were comparing apples to oranges when looking for differences between EPIRB's and PLB's.

GARY